Grinding tool



.Junve 18, 1.940. H, sCHNElDER 2,204,826

GRINDING TOOL Filed May 26, 1939 Aorneys.

Patented lune l, l

GRINDNG TOOL Berlin, Germany Application May 26, 1939, Serial No. 275,968 In Germany June 1, 1938 6 Claims.

This invention relates to a grinding tool similar to that disclosed inmyprior specication Serial No. 245,302,.and consists of an aluminium carrier, with grains of grinding material pressed into it. The invention also comprises a method of manufacturing such a grinding tool. The grains of grinding material may be diamonds, and are pressed into the carrier in such a manner that all their tips stand out freely above the surface of the carrier and are located exactly in an imaginary surface complementary to that which is to be ground by means of the grinding tool.

The present invention relates to the consolidation of the embedding of the grinding material in the aluminium carrier, and is characterised by an oxidation oi the embedding zone of the aluminium carrier, upon the surface portions of which, located between the grains of grinding material, a coating of oxide is provided, this layer of oxide extending from the surface into the interior of the carrier.

This invention renders it possible rstly to make the carrier from exceedingly soft aluminium, thereby simplifying the manufacture of v the grinding tool, and more particularly the pressing of the grains of grinding material into the latter. rihe oxidation makes the aluminium as a whole harder, and therefore stronger. The extent to which this method of strengthening is carried admits of being varied Within very wide limits, for it depends upon how far .the layer of oxide extends into the interior of the carrier. By the oxidation according to the invention, the embedding of the grains of grinding material is appreciahly consolidated, because the layer of oxide grows around the exposed corners and edges of the grains of grinding material after the latter has been pressed into the carrier. Furthermore the layer of oxide completely precludes the occurrence of cold welding, which is very liable to occur with aluminium between the workpiece to he ground and those portions of the surface of the carrier that are free from grinding material, thus obviating one disadvantage that makes itself particularly noticeable now andthen in grinding tools comprising an aluminium carrier, because the cold welding inevitably results in cracks and other injuries to the ground surface of the workpiece. The durability of a grinding tool according to the invention is great because the layer of oxide strengthening the aluminium carrier is very hard. This hardness can in a simple manner be increased to values which approach the hardness of carborundum.

This invention may advantageously be extended `face and on the unarmored surface.

to grinding foils. In the case of an aluminium foil armored with granular grinding material on one side only, a layer of oxide may extend into the interior of the foil both on the armored surn the limiting case the oxidation may be carried so far that an aluminium foil, armored on one side only or on both sides, is oxidized right through.-

The oxidation according to the invention may be eiected by any one of the methods in use that are found suitable. It falls within the ambit of the invention to produce the oxidation electrically or galvanically, for it has been found that this is particularly advantageous on three grounds. Firstly, by the distribution of the electric field,

`the aforementioned growth of the layer of oxide around the corners and edges of the-aluminium carrier is ensured in a particularly complete manner. Secondly, ithas been found that in the case of electrical or galvanic oxidation of the aluminium carrier of the grinding tools according to the invention, the depth of penetration of the layer of oxide into the interior of the carrier can be particularly simply and reliably regulated. Thirdly, a particularly hard layerof oxide can be produced upon and in aluminium carriers by electrical or galvanic oxidation.

The distribution of the electric held which is advantageous in the present caso in the neighhourhood of the di-electric grains of grinding material pressed into the aluminium carrier also occurs in the case of the galvanic production of a metallic coating. The invention utilizes this for a preparatory process preceding the oxidation, which, as stated, can be elected fundamentally by one of the known methods, but particularly advantageously by electrical or galvanic means, in such a manner that before the oxidation the surface portions of the aluminium carrier that are located between the grains of grinding material are galvanically provided with a coating of aluminium. Experience has shown that by this preliminary treatment and by the subsequent oxidation, particularly high-grade grinding tools according to theinvention can be produced, wherein the electrical or galvanic oxidation has again proved its special advantages.

The growth of galvanic deposits of metal around grains of grinding material has become known from a process by which grains of grinding material are cemented to one another and to a metallic plate. The grains of grinding material in that process lie upon one another in a number of layers, often a considerable number, and the galvanically produced metallic deposit, which .forms a sort of grid, is gradually used up when the grinding tool is in use.

If these metallic deposits were to be produced as aluminium deposits, the aforementioned cold welding would occur.

'Ihe invention is diagrammatically illustrated by way of example in partial sections on a greatly exaggerated scale in the accompanying drawing, in which Figure 1 shows a grinding tool with a thick aluminium carrier;

Figure 2 analuminium foil armored on one side with grinding material; and

Figure 3 an intermediate product at the stage preceding the oxidation.

In Figure l the crosshatched zone 5I represents the oxidation of the aluminium carrier I l, into which grains of grinding material ii have been pressed. Here the oxidation extends only a comparatively short distance into the interior of the carrier Il.

In the grinding foil shown in Figure 2, in addition to the layer of oxide 5l embracing the embedding zone of the grains of grinding material I1, another layer of oxide 5I starting from the under side of the aluminium foil 28, extends into the interior of the latter.

In Figure 3, 52 is a coating of aluminium applied galvanically to the surface portions it of an aluminium carrier which are located between the grains of grinding material Il, this coating being in other respects of any convenient form. It adheres firmly to the surface portions lli, and the subsequent oxidation operation may be carried out in such a'manner that not only is the galvanic coating of aluminium 52 converted into aluminium oxide, but the oxidation also extends through the coating 52 to the carrier itself.

What I claim is:

l. A grinding' tool consisting of an aluminium carrier and grains of grinding material pressed into the said carrier, the tips of all the grains of grinding material standing out freely above the surface of the carrier and being located in an imaginary surface which is equidistant from the carrier surface and is complementary in form tc the surface to be ground by the tool, and the embedding of the aluminium carrier comprising a layer of oxide consolidating the embedding of the grains of grinding material.

2. A grinding tool consisting of a carrier of aluminium foil and grains of grinding material pressed into one side of the said carrier, the tips of all the grains of grinding material standing eut freely above the surface of Vthe carrier and being located in an imaginary surface which is equidistant from the carrier surface and is cornplementary in form to the surface to be ground by the tool, a layer of oxide on the same side of the carrier as the grains of grinding material, this layer of oxide consolidating the embedding of the grains of grinding material in the carrier, and a layer of oxide on the other side of the carrier,

' this second layer of oxide extending. into the interior of the aluminium foil.

3. A method of manufacturing a grinding tool, consisting in forming on an aluminium carrier a surface complementary in shape to the surface to be ground by the tool, applying granular grinding material uniformly to the surface thus formed on the carrier, pressing the said granular grinding material into the aluminium carrier, and oxidizing by electrical means the surface layer'of the aluminium carrier in which the grains of grinding material are embedded.

4. A method of manufacturing a grinding tool, consisting in forming on a carrier of a'uminium foil a surface complementary in shape to the surface to be ground by the tool, applying granular grinding material uniformly to the surface thus formed on the carrier, pressing the said granular grinding material into the aluminium carrier, so that the tips of all the grains of grinding material stand out freely above the surface of the carrier and are located in an imaginary surface which is equidistant from the carrier surface, oxidizing by electrical means the surface layer of the aluminium carrier in which the grains of grinding material are embedded, and oxidizing by electrical means the other surfaces of the aluminium foil carrier, the layer of oxide produced on this other side extending into the interior of the aluminium foil.

5. A method of manufacturing a grinding tool,

consisting in forming on an aluminium carrier asurface complementary in shape to the surface to be ground by the tool, applying granular grinding material uniformly to the surface thus formed on the carrier, pressing the said granular grinding material into the aluminium carrier, oxidizing by electrical means the surface layer of the aluminium carrier in which the grains of grinding material are embedded, galvanically applying a coating of aluminium to the portions of the carrier surface lying between the grains of grinding material, and converting the coating of aluminium thus produced into aluminium. oxide.

(i. A. method of manuiacturing a grinding tool, consisting in forming on a carrier of aluminium foil a surface complementary in shape to the surface to be ground by the tool, applyingv granular grinding material uniformly to the surface thus formed on the carrier, pressing the said granular grinding material into the aluminium carrier, galvanically applying a coating of aluminium to the portions of the carrier surface lying between the grains of grinding material, converting the coating of aluminium thus produced into aluminium oxide, and oxidizing the other surface of the aluminium carrier.

HERMANN SCHNEDDER.

Sii 

